Method of forming heat exchanger fin collars

ABSTRACT

Method of forming integral extending collars from relatively thin aluminum alloy sheet material by incremental and composite flanging and ironing operations on portions of such sheet that overlie an aperture in a female die member by passage of a selectively sized and shaped punch therethrough.

1 51 Sept. 26, 1972 METHOD or FORMING Il-IEAT United States Patent McKee et a1.

B58781 34445 3 33333 %UNUWH 77777/ n H u u 1 m I m m m e m m m flma rnr. Z wlnee .H h h fl fU O a KBSBSHP 774 20 6922667 9899999 1111111 446692 8592234 456 32 1 1 15 7066900 78 9929 R 2 233 i 8 8 M eon 9. 5 8 U] I. r. V" .e v F Hm 26 m S204 R ,m, A whml L M Il L Ced OMK C H nwa e m. n N A .d r b a nu Efi s GFDRDI N. .S- A .1 H m C m X V El .l 2 M 7 l Primary Examiner-Richard J. Herbst Attorney-Robert E. lsner and Peter J. Franco relatively thin aluminum alloy sheet material by incremental and composite flanging and ironing operations on portions of such sheet that overlie an aperture in a female die member by passage of a selectively sized and shaped punch therethrough.

March 29, 1971 211 Appl. No.2 128,694

113/118 c, 72/348, 29 1573 B .8211! 19/08 113/118 0, 118 R; 165/158; 1 29/1573 B; 72/348 References Cited UNITED STATES PATENTS Kern et al. .............1'13/118 c 221 Filed:

Related U.S. Application Data [63] Continuation-impart of Ser. No. 45,341, June 11, 1970, abandoned, which is a continuationin-part of Ser. No. 748,725, July 30, 1968, abandoned.

[52] U.S. Cl. [51] Int. [58] Field ofSearch.......

PATENTEDSEPZS 1912 SHEET 1 [IF 2 INVENTORS FRANCIS c. McKEE BY ROGER c. HADDON ATTORNEY PATENTEDSEPZB I912 3.693; 568

SHEET 2 [1F 2 INVENTORS FRANCIS G McKEE BY ROGER C. HADDON tu eiiu ATTORNEY METHOD OF FORMING HEAT EXCHANGER FIN COLLARS This is a continuation-in-part of application Ser. No. 45,34l filed June 11, 1970, now abandoned, which is in turn a continuation-in-part of application Ser. No. 748,725 filed July 30, 1968, now abandoned.

This invention relates to the deformation of aluminum alloy material and particularly to an improved method for forming integral extending cylindrically shaped collars from relatively thin, work hardened, aluminum alloy sheet material.

The formation of such integral extending collars in aluminum alloy sheet material is desirably included in the fabrication procedures, for example, of collar type heat exchanger fins. Present commercial fin forming practice generally effects such integral collar formation by incremental stretching of aluminum alloy having high tensile elongation values through a number of discrete forming operations. Alloys having tensile elongation values of percent or more are usually required and as many as six to 10 separate operations on annealed material are oftentimes required to produce satisfactory collar heights.

It is desirable for aluminum alloy sheet from which integral extending collars are formed to have relatively high yield strengths so that the unformed fins as well as the collars formed from such material, will not be readily damaged by accidental contact with other objects. This is particularly true with relatively thin fin stock material. With the methods heretofore practiced, however, it has been difficult, if not commercially impossible, to form such collars in desired dimensions from thin work hardened sheet without undue splitting of the collars. In fact, integral extending collars have typically been formed from sheets of annealed material of high elongation in order to facilitate forming and avoid splitting the collars, yet provide resistance to damage. Accordingly, it is desirable to ptovide a method of forming integral extending collars from work hardened material so that thinner material can be utilized with adequate resistance to damage. It is also desired to provide a method of forming such collars from work hardened material to a height which has not previously been possible.

In its broad aspects the subject invention embodies an improved method for deforming relatively thin, work hardened aluminum sheet by unitary displacement of a selectively sized and shaped punch member through selectively sized coaligned apertures in the sheet material and an underlying female die member to incrementally and compositely flange and iron the portions of said sheet material overlying the aperture in the female die member. In its more specific aspects, the subject invention provides a new method of forming collar type heat exchanger fins from work hardened aluminum alloy material substantially independent of the tensile elongation values thereof and which are markedly free from splits and are characterized by greater collar heights with usable wall thickness and greater ratios of collar height to hole :diameter than have been heretofore obtainable from work hardened sheet by conventional fin forming techniques.

Among the further advantages attendant practice of the herein disclosed method are the obtaining of satisfactory flatness of the formed parts because of the limited locus of deformation thereof; a utilization of hard and intermediate temper materials; reduced tooling and maintenance costs attendant the reduced number of required operations and the permitted obtaining of variable collar heights from given stock thicknesses through variation in the degree of ironing effected during the single deformation operation.

Included among the objects of this invention is the provision of a new method of effecting the deformation of relatively thin, work hardened, aluminum alloy sheet material advantageously utilizable in the fabrication of collar type heat exchange fins.

Other objects and advantages of the subject invention will become apparent from the following portions of this specification and from the accompanying drawings, which delineate, by way of illustrative example, the nature of a presently preferred sequence of operations incorporating the principles of the invention in the fabrication of collar type heat exchange fins.

Referring to the drawings:

FIG. 1 is a sequential schematic sectional view illustrating successive operations performed on relatively thin work hardened aluminum alloy sheet in the formation of collar type heat exchanger fins;

FIG. 2 is a sectional view of a die and punch assembly that may be employed in the practice of the methods herein disclosed.

FIG. 3 is an enlarged elevational view illustrating desirable proportional dimensional relationships that may be employed in the practice of the methods of this invention.

FIG. 4 is a vertical sectional view of a sheet having a plurality of collars formed therein.

Referring to the drawings and initially to FIG. 1 thereof, the formation of collar type heat exchanger fins through utilization of the hereindescribed method requires the initial introduction of a selectively shaped and sized aperture 10, preferably of a generally circular configuration, in a relatively thin sheet 12 of work hardened aluminum alloy. The portions of the sheet 12 immediately surrounding the aperture 10 are then incrementally and compositely flanged and ironed, through the hereinafter described method, to selectively deform the same into a depending collar 14 of a wall thickness that is sensibly less than that of the undeformed sheet material 12. The length of the extending collar 14 is then trimmed to a predetermined desired height and the mouth thereof is flared, as at 16, to a required desired diameter and contour.

As shown in FIG. 2, the selective deformation of the portions of the sheet 12 immediately surrounding the aperture 10 is preferably effected by preliminarily locating the sheet material 12 on a tool block 20 with the aperture 10 therein disposed in substantial coaxial alignment with a complementally shaped aperture defined by the bore of a female die member 22 mounted therein. Disposed in overlying relationship with the tool block 20 is a second or top tool block 24 having a complementally shaped and selectively sized punch member 26 mounted thereon and displaceable in conjunction therewith. Positioned intermediate the upper and lower tool blocks 24 and 20 respectively is a stripper and hold down plate member 28 that is normally biased into compressive engagement with the upper surface of the sheet 12 by spring members 30, 32.

As will now be apparent, the cross-sectional extent of the bore of the female die member 22 will be determinative of the exterior dimensional extent of the collar 14. In accord with the principles of this invention, the cross-sectional extent of the aperture in the sheet 12 is preselected so as to be at least two-thirds of that of the bore of the female die member 22. In addition and as best shown in FIG. 3 the complementally shaped punch member 26 is of varying cross-sectional extent along its longitudinal axis and is shaped to provide a base portion, generally designated 41, diametrically sized to readily pass through the aperture 10 in the sheet 12, an upper and ironing tool portion generally designated 42, of maximum diametric dimensions less than that of the aperture defined by the bore of the female die 22 but greater than the difference between the diametric extent of said female die defined aperture and twice the thickness of said aluminum sheet material and a portion of uniformly and gradually increasing cross-sectional extent. As best shown in FIG. 2,'the upper defining edge 34 of the female die member and the periphery 36 of the punch 26 at the locus of maximum diametric extent are rounded to provide for gradual, rather than abrupt dimensional transition.

In the fabrication of collar type heat exchanger fins, relatively thin hard or intermediate temper aluminum alloy sheet is positioned as illustrated in FIG. 2 and described above. The aperture 10 in the sheet 12 and the larger aperture defined by the bore of the female die member 22 are of circular configuration and the punch member 26 is shaped in the nature of a truncated conical section having its dependent end of lesser cross-sectional extent than the upper end thereof. Advance of the punch member 26 initially effects introduction of the dependent end thereof into and through the aperture 10 in the sheet 12 and, upon continued advance thereof, in consequent initial engagement of the defining edges of the aperture 10 in the sheet 12 with the intermediate portion of continually increasing extent of the punch member 26 which automatically effects accurate coaxial alignment therebetween and with the base of the female die member 22 prior to the initiation of deformation. Continued advance of the punch member 26 effects a substantially uniformly increasing and gradual deformation of the portions of the sheet 12 overlying the aperture defined by the bore of the female die member 22 characterized at least in part by an incremental and composite flanging and ironing operation as the upper portion of the punch member abuts the entrance of and passes through the bore of the female die member 22 to form an integral extending collar 14 of marked height and decreased wall thickness.

As shown in FIG. 3 the preferred configuration for the punch member 26 is that of a truncated conical section having an intermediate body portion 40 whose linearly configured side walls increase in cross-sectional extent as determined by an angle of about 10 relative to the longitudinal axis thereof and with angles of about 10 to 30 being suitable. By way of illustrative example, the following tabulation sets forth preliminary results obtained through use of punch members shaped as shown in FIG. 3 having an effective length of thirteen thirty-seconds inch from the base to the locus of maximum diametric extent thereof in association with a female die member 22 having a bore of 0.402 inch in diameter for various aluminum base alloy sheets in a state resulting from cold reduction, e.g. rolling, of at least percent of the thickness of fully recrystallized, e.g. annealed, stock known as H19 temper and of varying gauge and with various dimensions for the aperture 10 therein:

TABLE] Aluminum Sheet Sheet Maximum Collar Alloy & Thickness Aperture Diameter of Height Temper lnches Diameter Punch Member Inches The nominal composition of the alloys tabulated above is generally as follows, with the remainder thereof being constituted by normally present impurities and aluminum:

3003 0.12% Cu, 1.2% Mn 5086 0.45% Mn; 4.0 Mg, 0.10 Cr With respect to temper, the method of the invention can be utilized advantageously in the fabrication of integral extending collars from work hardened aluminum alloy sheet of either hard or intermediate temper. Intermediate temper aluminum alloy materials such as 7072-H14, 3003-1112 and H14, and 11004114 have substantially higher yield strengths than do fully annealed or 0 temper materials, and will provide high strength fin stock even in thin sheet form, e.g. sheet material 0.003 inch to 0.020 inch in thickness. For example, 3003-H12, an intermediate temper aluminum alloy product resulting from cold reduction of approximately 20 percent of the thickness of an annealed stock, has a typical yield strength of 18,000 pounds per square inch (psi) as compared to 6,000 psi yield strength for annealed material (3003-0), and 27,000 psi for full hard material (3003-H18). Data provided by the Aluminum Association indicates that for wrought products, the yield strength for one-quarter hard aluminum alloy product will be at least one-half the yield strength for the same alloy product in a full hard condition, and two or more times the typical yield strength for the product in a fully annealed or recrystallized condition. Intermediate temper products are, therefore, sufficiently hard to produce high strength fins, and yet may be formed into relatively high substantially split free integral extending collars when fabricated by the method of the present invention. However, such products have generally been considered to be too hard to have been formed into such fin collars by the methods heretofore known, and could not be formed to the collar heights that are made possibit: by the method of the present invention.

Although fin collars have apparently previously been formed in soft sheet material by one-step flanging and ironing methods, commercially satisfactory methods have not been available for flanging and ironing collars on thin work hardened aluminous material to the relative heights of the collars set forth in Table l. The disclosed prior methods have not only utilized-relatively thick and soft apertured sheet material, but also apparently, have been used only to form relatively short collars. The expression relatively high collars as employed herein is used to describe collars which extend from the plane of the sheet for distances in the range of 12 to 30 times the thickness of the sheet for collars in the order of three-eighths inch in diameter, up to as much as 45 times the thickness of the sheet for collars which are in the order of one-half inch in diameter, and even higher for larger diameter collars. The method of the invention thus renders possible the production of collars which are substantially higher than those of prior one-step flanging and ironing methods which have produced collar heights of a usual maximum of only 3 to 6 times the sheet thickness for collars which are approximately one-fourth inch or more in diameter.

In forming split-free relatively high fin collars in work hardened aluminum sheet material as set forth in Table I, the percent ironing which is effected in the herein described one-step flanging and ironing operation, is attended with an appreciable degree of criticality to the forming process. In accordance with this invention, the material which is formed into the collars by the single step operation desirably must be ironed or reduced in thickness by at least 45 percent, and is preferably reduced in thickness in the range of 60 to 70 percent, in order to avoid undue splitting thereof. Although ironing reductions of over 45 percent have previously been accomplished, there is nothing that indicates any awareness that employment of such higher percent reductions is a material, if not a critical factor, in being able to effectively form split-free collars in work hardened aluminum alloy sheet material. Since it is easier to effect a lower'percent of ironing, and since no significant importance has been heretofore attached to effecting a higher percent of ironing in a single flanging and ironing step, antecedent use of such higher percentages of ironing reduction has been generally limited to relatively thick gauge soft material using relatively small pierced or cut apertures in the material and for the forming of relatively short collars, e.g. as shown in US. Pat. No. 2,157,354. The results obtained herein through use of these higher reductions on thin work hardened aluminum sheet material was both unusual and unexpected. In fact, the reasons why these surprising results are obtained are even yet not fully understood, although it is believed that possibly in some way the compressive stresses and/or metal displacement produced by the higher reductions in some way counteract or ameliorate the tensional stresses which are produced in the material around the pierced edge of the collars when this material is stretched during flanging. It has been observed that when relatively high collars are formed in work hardened aluminous material by one-step flanging and ironing involving less than 45 percent reduction, undue splitting occurs. For example, experience to date seems to indicate that if exactly the same materials and types of tools were used as those set forth in Table l, except that ironing is done in two steps using two punches, with the first punch flanging and ironing the collar less than 45 percent and the second punch completing the ironing to the degree effected in the examples in the table, the collars would be subject to undue splitting.

Referring again to Table I, die clearance between the punch and die aperture can be calculated by subtracting the maximum punch diameter from the diameter of the die aperture and dividing the result by 2 (annular clearance around the punch). The percent ironing or reduction can then be closely approximated by subtracting the die clearance from the thickness of the sheet which is being worked and dividing the result by the sheet thickness. For the examples in Table I, computation of the percent ironing shows a range between approximately 55 and percent, although the method can be practiced using one-step reductions as low as approximately 45 percent for some materials and hole sizes. The upper limit is considered to be a practical limit as to reductions which are ordinarily possible to be made in one step without tearing the collar from the base material.

In forming collars in sheet material in accord with the principles of this invention, the diameter of the aperture in the sheet is determined, at least in part, by the diameter of the collar to be formed. In contradistinction to the teachings of the prior art, which indicated that the diameter of the aperture should be relatively small in comparison with the diameter of the collar to be formed so as to make available or bring as much material as possible into the collar, the method of the present invention utilizing a high degree of ironing, requires that the diameter of the aperture be relatively large in comparison with the diameter of the collar to be formed, as for example two-thirds or more, and yet such method produces higher collars than were heretofore thought possible.

It should be noted, however, that, while the present method utilizes relatively large apertures in the sheet material, such apertures cannot be made so large that there is available insufficient metal to be formed into the collar. In order to produce the relatively high collars desired for heat exchanger applications, the diameters of the apertures in the sheet should preferably not be over seven-eights of the diameter of the aperture in the die for forming such collars.

Based on the foregoing, it seems apparent that the subject method has applicable utility utilizing various types of aluminum alloy materials of thicknesses varying from 0.003 up to, for example, about 0.020 and for hard and intermediate tempers having yield strengths at least one-half the yield strength of the same material in a full hard condition. It is likewise apparent that while the subject method has found marked utility in the formation of cylindrically shaped collars from circularly shaped apertures, the incremental and composite flanging and ironing operation may be utilized to produce high collars around openings that depart, at least in some degree, from the circular openings specifically described herein.

FIG. 4 illustrates the nature of the resultant product wherein a plurality of cylindrical collars 14, each having a flared terminus 16, integrally extend in predetermined spacing and alignment from a common sheet 12 of relatively thin aluminum alloy.

As will be apparent from the foregoing, practice of the herein described method has effected the production, by a single operation on relatively thin work hardened aluminum alloy sheet, of an improved product possessing, inter alia, markedly higher ratios of flange height to hole diameter than has been heretofore obtainable. Such increase in collar length is directly attributable to the effecting of reductions in wall thickness of up to and over 60 percent, and well over the value of about 3540 percent that is recommended for conventional ironing operations.

Having thus described our invention, we claim:

1. In the fabrication of integral extending collars from relatively thin aluminum alloy sheet material, the steps of coaxially aligning a selectively shaped aperture in a female die member sized to define the exterior dimensional extent of said collar member with a complementally shaped aperture in a sheet of relatively thin work hardened aluminum alloy of at least intermediate temper sized to have a minimal cross-sectional dimension at least equal to two thirds of that of the aperture in said female die member and unidirectionally advancing a complementally shaped apertures to incrementally and compositely flange and iron the marginal edge portions of said sheet material overlying said aperture in said female die member to reduce the thickness of the marginal edge portion thereof by at least 45 percent and form an extending essentially split-free collar that extends from said sheet material a distance equal to at least 12 times the thickness of said sheet material.

2. The method as set forth in claim 1 in which said marginal edge portions of said sheet material overlying said aperture in said female die member are reduced in thickness in a range of between 60 and percent to form said collar.

3. The method as set forth in claim 1 wherein said sheet of aluminum alloy has a yield strength at least one-half the yield strength the sheet would have in a full hard condition.

4. The method of claim 1 wherein the sheet engaging portions of said punch member are disposed at an angle of from about 10 up to 30 relative to the longitudinal axis thereof.

5. The method of claim 1 wherein the sheet engaging portions of said punch member are of truncated conical configuration.

6. The method of claim 1 wherein the sheet engaging portions of said punch member are of truncated conical configIuration having a vertex angle of about 10.

7. he method of claim 1 including the step of restraining displacement of the portions of the sheet adjacent to said aperture therein during the advance of the punch member therethrough.

8. The method as set forth in claim 1 wherein the apertures in said sheet and die member are of circular configuration and said sheet engaging portions of said punch member are of truncated conical configuration having a vertex angle of about 10. 

2. The method as set forth in claim 1 in which said marginal edge portions of said sheet material overlying said aperture in said female die member are reduced in thickness in a range of between 60 and 70 percent to form said collar.
 3. The method as set forth in claim 1 wherein said sheet of aluminum alloy has a yield strength at least one-half the yield strength the sheet would have in a full hard condition.
 4. The method of claim 1 wherein the sheet engaging portions of said punch member are disposed at an angle of from about 10* up to 30* relative to the longitudinal axis thereof.
 5. The method of claim 1 wherein the sheet engaging portions of said punch member are of truncated conical configuration.
 6. The method of claim 1 wherein the sheet engaging portions of said punch member are of truncated conical configuration having a vertex angle of about 10* .
 7. The method of claim 1 including the step of restraining displacement of the portions of the sheet adjacent to said aperture therein during the advance of the punch member therethrough.
 8. The method as set forth in claim 1 wherein the apertures in said sheet and die member are of circular configuration and said sheet engaging portions of said punch member are of truncated conical configuration having a vertex angle of about 10*. 